Apparatus and method for heating solid surfaces

ABSTRACT

The heating of solid surfaces by grids of fine line is made balanceable and controllable by building into the grid a network of resistances which can be altered at will by the severance or introduction of current carrying conductors which form part of the grid.

Feb. 4, 1975 United States Patent [191 Schafer et al.

[56] References Cited UNITED STATES PATENTS APPARATUS AND METHOD FORHEATING SOLID SURFACES 338/195 X 338/195 X 219/203 X ,597,674 5/1952R0bbins........... 3,094,678 6/1963 Eisler........ 3,288,983 11/1966Lear, Sr. 3,313,920 4/1967 Gallez.............. 3,414,713 12/1968Reifeiss et 211.... 3,621,441 11/1971 Hudnall [22] Filed: Sept. 27, 1972[21] Appl. No.: 292,770 Primary Examiner-C. L. Albritton Attorney,Agent, or FirmPennie & Edmonds [30] S Fggeilgg7llkppllcatlon PriorityData ABSTRACT The heating of solid surfaces by grids of fine line isFrance.............................. 71.35161 made balanceable andcontrollable by building into 219/203 219/522 338/195 the grid a networkof resistances which can be altered at will by the severance orintroduction of current carrying conductors which form part of the grid.

[58] Field of Search 219/203, 522, 543, 549; 338/195, 307-309 6 Claims,7 Drawing Figures This invention relates to the heating of surfaces by Iresistance grids. It is particularly concerned with an apparatus and aprocess for balancing the electrical resistance of heating grids appliedto vehicle windows. Such grids include conductive lines applied to thewindow, of such fineness as not to impair vision, which are connected tobus bands which receive their current from a battery or other source andwhich are advantageously composed of a frit of glass and metal fusedonto the surface of the glass.

Several processes of manufacturing such heated windows are known. In onewhich is much used an electrically conductive metallic paste capable ofbeing fused is applied to the surface of the glass in an appropriatedesign, for example application may be by the silk screen technique,after which the assembly is baked at high temperature. In all suchapplications by impression or coating, difficulty has been experiencedin producing with certainty a thickness of layer or width of line whichis constant. For example, in applying heating resistances there aredepartures from one screen to another and it follows that during thecourse of production the width of the heating bands, which is on theorder of .5 mm., varies. A certain number of factors are reponsible forthese variations of section, for example the viscosity of the pastewhich is being applied, variations in room temperatures, speed ofapplication, and the state or physical condition after usage of the silkscreen or other apparatus of application. Even in taking severeprecautions, it is not possible in industrial practice to maintain allof these factors absolutely constant and slight variations appear in thesection of the conductors and entrain similar and undesirable variationsin the electrical resistance of the heated windows thus produced.

It is an object of this invention to produce heating grids on solidsurfaces within close tolerances, that is to say, producing resistancevalues and heated effects as precise as possible. Heretofore it has beenproposed to reinforce the heating conductors after baking, byelectroplating in order to achieve that desired degree of conductabilitybut that process is complex and expensive.

The present invention achieves its objects by means for heating a solidsurface including a resistance grid, comprised of thin resistance linesand bus bands, composed of severable, conductive material fused to thesolid surface, said grid comprising a plurality of electricallyconnected parts capable of separation or interconnection to change theresistance of the part thereof which supplies the resistance lines, andmeans electrically attached to the bands to pass current through thebands and the lines; and by a method of establishing a current patternin a heating grid which comprises fusing a grid comprised of lines andbus bands to a solid surface and excising parts of the bus bands toestablish the desired pattern.

In the region of the window occupied by the bus band or in the regionwhere the heating lines are attached to the bus bands there are appliedto the surface conductive figures which can be severed in particularparts so as to change the current supplied to the heating lines. Thesefigures have parts or branches which can be readily cut to remove someof the material so as to lengthen or shorten the particular coursethrough which the current flows to reach the heating lines.

Due to the present invention the use of electroplating is eliminated andas a consequence, the heating lines, after baking, are of suchaccurately constructed resistance as to be within the limits oftolerance requiring no supplemental treatment. The correction of theelectrical resistance of windows which do not conform to the requiredtolerances in the first instance is made easy by this invention becauseit suffices to change the conformation of the bus bands or otherconductors which supply the heating lines.

Notably, the electroconductive layer, for example the bus band figure,can be cut in one or more regions with the aid of an appropriate tool,so that the current will be obliged to follow a longer path, whichwillincrease resistance. it is also within the invention to provide suchwindows by normal procedure with bus band figures which will only beshort-circuited when it be-, comes necessary to lower the resistance,but the preceding construction is usually simpler. ln general, itsuffices in the first instance to prepare windows of which theresistance is close to the lower limit, while additional resistances areprovided in shunt and, consequently, out of the path of the current,these resistances being put in circuit as desired by cutting in theshunts when an increase in the resistance becomes necessary.

Following a first form of the invention, at least one of the bus bandsis provided with internal gaps, for instance longitudinal slits,arranged so that the conductive material on both sides of the slit maybe removed inappropriate locations. Whenever the current input issituated at one end of the bus band one may use a single slit; toincrease the electrical resistance the bus band can be cut between theslit and the heating conductors at a location somewhere between thecurrent input and the base of the heating lines. When the current inputis placed in the middle of the bus band it is recommended to provide twolongitudinal slits which are to be separated by a conductive part of thebus band. If an increase in resistance becomes necessary the bus band iscut between the slits so that the direct passage of current from thepoint of input to the portion of the bus band situated between theincision and the heating lines will be interrupted.

When relatively large corrections of electrical resistance are to beproduced, one may according to another form of the invention provide thebus bands with several slots placed side by side and substantiallyparallel to one another, extending up to the ends of the bands,establishing in one or more of the strands, by cutting, separationswhich result in a conformation such that the total length of theadditional resistance can represent several times the length of the busband itself.

A finer adjustment of the resistance may be obtained by subdividing thelongitudinal slots into a series of aligned slots between which a seriesof bridges of conductive material are left which can be individuallysevered in variable numbers according to need.

According to a variation of the invention, one may provide in theimmediate vicinity of the junction between the heating lines and the busbands some supplementary figures which affect only a limited number oflines. These figures are advantageous networks of conductors parallel tothe bus band properly so called and at a short distance from them. lf anincrease in the resistance becomes necessary this network is cut inimmediate proximity to the bus bands so that the current is obliged tofollow a longer path, which may be composed of one or several lines ofwhich the greater or lesser number may be made to carry the heatingcurrent.

The above and further objects and novel features of the presentinvention will more fully appear from the following detailed descriptionwhen the same is read in connection'with the accompanying drawings. Itis to be expressly understood, however, that the drawings are for thepurpose of illustration only and are not intended as a definition of thelimits of the invention.

In the drawings wherein like reference characters refer to like partsthroughout the several views;

FIG. 1 is a plan view of a first and major form of the invention asembodied in the rear light of an automobile;

FIG. 2 is a partial view of a modification on an enlarged scale;

FIG. 3 is a partial view of a further modification;

FIG. 4 is a partial view in plan ofa third modification;

FIG. 5 is a partial view in plan of a further modification; and

FIGS. 6 and 7 are partial views in plan of variations of the fifthmodification.

FIG. 1 represents a heated vehicle windshield 1 on the surface of whichhave been applied lines of heating resistance 2 which are composed ofacomposition containing a proportion of conductive metal. Suchcompositions are known and need no description; they are applied by thesilk screen method and baked onto the surface of the glass at atemperature around 600C. The resistive heating conductors 2 areconnected at their extremities to bus bands 3, which are advantageouslycomposed of the same material as the lines 2 and may be applied to thewindow in the course of the same operation as the lines. Upon the busbands 3 are soldered the current inputs 4-4 which carry contacts 5 towhich the input and output current lines are attached. The bus bands 3have elongated slots 6 which extend throughout the extent occupied bythe lines 2. The slots 6 are obtained by masking that area during thesilk screen operation so that in that region the conductive metallicpaste does not touch the surface of the glass and thus divides the busbands into two strips 3a and 3b which are connected at their ends. Thewidth A of the inner of these strips 3a is chosen so that it alone willcarry the heating current to the lines 2 without opposing anysubstantial resistance to its flow. The exterior strip 3b is narrowerand has a resistance to the heating current which is about 5 percent ofthe overall resistance of the grid. The heating current therefore flowsessentially through the inner strips 3a and the lines 2. This flow isindicated by the arrows P. If it appears that the overall resistance ofthe heating unit is too low, one of the strips 3a or both bands 3a canbe cut at 7 near the lower extremity of the slot 6. Because of the cutwhich extends through to the slot the current follows a different pathand flows through strip 3b, or through both strips 3b when a double cutis made, following the direction of arrows P. When a small increasein.the resistance suffices one is content to make the cut 7 in only oneof the bus bands. If the cut 7 is made in both bus bands, the increasein resistance is doubled. In some cases, the widths B and B' of theexterior strips may be different. When, by the foregoing method, one

does not wish to increase the resistance the mode of operation may bechanged so that the change in the electrical resistance involves adiminution. In this case, the cuts 7 are made in advance during themanufacture of the windshield and are later short-circuited, producing adiminution. Short-circuiting can be accomplished by applying some tinsolder. It is equally possible to make in advance a cut in only one ofthe two bus bands. The

overall resistance of a heated window thus made can thus be eitherincreased by making a cut in the inner strip which feeds the lines or itcan be reduced by shortcircuiting the break initially introduced in thefirst bus band. Thus, the overall resistance can be corrected in bothdirections.

FIGS. 2 to 4 represent advantageous variations of the same principle. Inthe form represented in FIG. 2 the input contact 14 is located in themiddle of the length of the bus band 13. Slots 16 are provided above andbelow the contact. The heating current flows principally along the innerstrips 13a in the directions of arrows Q but if one makes cuts 17 asindicated in dash lines, the current is forced to flow along paths Q,along the outside strips, around the ends of the slots and along strips13a and 13b thus increasing the length of the path and the resistance.According to the dimensions given to strips 13b the electricalresistance-may be thus increased in a predetermined degree.

In FIG. 3 the bus band 23 contains a series of aligned slots 26 and thisconstruction makes for greater facility of adjustment. In the drawing,each heating conductor 2 is opposite one of the slots. If one makes cuts27 through the inner strips the current is compelled to flow throughouter strips 23b, around the ends and then along the inner strips toreach the heating lines. Now, by making one or more cuts 28 between theslots one can make slight variations and achieve a high degree ofmodification in the resistance approaching each line and secure a fineadjustment of the current supply.

FIG. 4 is a modification which enables one to increase the overallresistance greatly. The bus band 33 has two parallel slots 36 and 36which divide the bus band into three conductive strips 33a, 33b and 330.Initially the flow of current from the contact 34 will be along theinner strip 33a to the'heating lines 2 but by making the cut 37 thecurrent will be compelled to flow through 33c toward the top of thefigure and over to 33a. If a still further increase in resistance isdesired the cut 38 can be made, which will require the current to flowalong the path of the arrow R through strips 330, 33b and 33a. It willbe observed that in each of FIGS. 1 to 4, and also in FIG. 5, the busbands are broader than the conductors 2 (42 in FIG. 5).

FIGS. 5 to 7 show modifications in which the supplementary resistancesare involved individually with the heating lines 42. The slots 44 aremade near the inner border of the bus band in alignment and opposite theheating conductors. The heating conductors are connected to the bus bandoff center of the slots. Only a small part of the heating current passesthrough the longer branches 44 which now may be inserted one by one intothe circuit of the heating conductors. If cuts are made along the lines45 in this way it will not only correct the overall resistance of theheating grid but may also correct the resistance of a particular heatingline, thus achieving the maximum possible flexibility of control. Thisflexibility of control can be increased by adopting the structures ofFIGS. 6 and 7.

In the form shown in FIG. 6, the bus band 53 is directly connected tocentral heating conductor 52 but is connected to the upper and lowerheating conductors through a network of multiple strands 54a and b whichare in series with their respective heating conductors. By making cuts55a one puts the line 54a into the circuit and by making the cut 55b oneaids the resistance of line 54b.

FIG. 7 exemplifies a network of lines 64a, b, c which are initiallyprovided with gaps as shown in the lower end of the two networks. Thebus band 63 thus delivers its current through a network of threeparallel conductor to heating line 62. If one wishes to reduce theresistance one may make one or more solderings at 65a and 65b asindicated in the upper part of the figure eliminating one or more of thecurrent-carrying parallel lines. if one applies tin solder at 65a theline 64a is cut out of the circuit. [f the gap 65b is alone closed, thetwo conductors 64b and 64c are cut out of the circuit, and if both gapsare closed at 65a and 65b all three lines 64a, 12 and c are eliminatedfrom the circuit.

The following example illustrates the invention. It relates to the rearlight of an automobile operating with the following characteristics:

Supply Voltage U 12 V Power Needed W,,, 150 W Maximum Power Consumable Wl80 W if the heating circuit has a resistance R and is operateddirectly, the power consumed is expressed by the formula W U /R fromwhich one may deduce the permissible limits at the resistance of thewindow and its manufacturing tolerance AR R s U /W 144/150 0.960,

R U /W 144/180 0.80 which is to say that AR t 0.080,, or 9.1 percent.

If one mounts a corrective resistance r in series, which reduces theintensity of the heating current, one derives the following formulas:

For the total power consumed For the power useful in heating m WM Now,therefore,

R r z U /W 144/180 0.80 with (R/R r) W,,,/W 150/180, that is to say r s0.2 R from which one derives Rs 0.67!) and consequently AR 2*: 0.1450,which is to say 18 percent, which establishes the fact that thetolerance of manufacture has been practically doubled.

This invention has been described in its application to the heating of awindow or a light of an automobile but it is to be understood that thesame principles are applicable to the control of the heating of anysolid surface to which the grid can be applied including plates, wallsand panels.

As many apparently widely different embodiments of the present inventionmay be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments.

What is claimed is:

l. A window comprising a transparent sheet, a plurality of opaqueresistive conductors substantially coextensive in length adhered inspaced substantially parallel relation to a surface of the sheet, saidconductors having a width small compared to their spacing, at least twobus bands made of electrically conductive material and having a widthwider than said conductors, said bus bands adhered to said surface ofthe sheet and connecting said conductors electrically in parallel, acurrent terminal connecting to each of said bus bands, and at least oneof said bus bands having elongated aperture means therethrough extendinglengthwise of said bus band with an end of said aperture means close tosaid terminal, said conductive material being removable selectively fromsaid sheet whereby upon said selective removal over a path extendingfrom said aperture means to the outer periphery of said at least one busband the current path between the current terminal connecting to said atleast one bus band and said conductors will be increased in length.

2. A window according to claim 1 in which said aperture means defines insaid one bus band two elongate conductive portions of unequal width.

3. A window according to claim 1 wherein each said terminal connects toone of said bus bands in the region of one end, and said elongatedaperture means comprises at least one slot.

4. A window according to claim 3 wherein said elongated aperture meanscomprises a pair of slots, one of said slots extending between pointscloser to and further from said terminal than any one of saidconductors, the other of said slots being arranged parallel to said oneslot ahd having a length less than said one slot, and wherein saidconductive material is removed from said bus band between said one slotnear said closer point and said periphery of said bus band.

5. A window according to claim 4 wherein additional conductive materialis removed over a path between an end of said other slot remote fromsaid terminal and said bus band periphery to further increase thecurrent path between said terminal and said conductors.

6. A window according to claim 1 wherein each of said terminals isconnected to said bus bands between the ends, and said elongatedaperture means includes at least two individual slots, at least one ofsaid slots being arranged to one side of said terminal and at least oneof said slots being arranged to the other side of said terminal, andsaid selective removal of conductive material from said sheet beingcarried out over paths each extending substantially from a proximal endof each slot closest to said terminal to said periphery of said bus bandto increase the current path between said terminal and said conductors.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIO PATENT NO. 3,86g5u5 DATED February 4, 1975 INVENTOR(S) Wolfgang Schafer and HelmutBrook It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 5, line 1 for "line" substitute --conductor--;

line L rewrite the equation as follows: U /(R r)- line 46, rewrite theequation as follows: --w WMR/(R r)-'-;' v

m line 51, rewrite the left-hand limb of the v inequality as follows:-R/(R r)--.

' Column 6, line 41 (claim line 6), for "ahd" substitute --8.nd-

Signed and sealed this 29th day of April 1975.

(SEAL) Attest v c. MARSHALL DANN RUTH C. MASON 1 Commissioner of PatentsAttesting Officer and Trademarks 1 UNITED STATES PATENT OFFICE 7CERTIFICATE OF CORRECTIO PATENT NO. 3,86 +,5 r5 DATED February L, 1975|NVENTOR(S) 1 Wolfgang Schalfer and Helmut Brook It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below;

Column 5,- line 1 for "line" substitute --conductor---;

line A rewriteth'e equation as follows:

--w- U /(R +"r)-:; A

M line 46, rewrite the equation as follows: --w WMR/(R r.)-'-; A

In line 51, rewrite the left-hand limb of the inequality as follows:--R/(R r)--.

' Column 6', line 41 4 (claim f, line 6), for "ahd" substitute --a.nd--.r A

Signed and S aled this 29t day of A ril 1975.

(SEAL) Attest: j j

. A c. MARSHALL DANN RUTH C. MASON i 1 Comissioner of Patents AttestingOfficer and "Trademarks

1. A window comprising a transparent sheet, a plurality of opaqueresistive conductors substantially coextensive in length adhered inspaced substantially parallel relation to a surface of the sheet, saidconductors having a width small compared to their spacing, at least twobus bands made of electrically conductive material and having a widthwider than said conductors, said bus bands adhered to said surface ofthe sheet and connecting said conductors electrically in parallel, acurrent terminal connecting to each of said bus bands, and at least oneof said bus bands having elongated aperture means therethrough extendinglengthwise of said bus band with an end of said aperture means close tosaid terminal, said conductive material being removable selectively fromsaid sheet whereby upon said selective removal over a path extendingfrom said aperture means to the outer periphery of said at least one busband the current path between the current terminal connecting to said atleast one bus band and said conductors will be increased in length.
 2. Awindow according to claim 1 in which said aperture means defines in saidone bus band two elongate conductive portions of unequal width.
 3. Awindow according to claim 1 wherein each said terminal connects to eachof said bus bands in the region of one end, and said elongated aperturemeans comprises at least one slot.
 4. A window according to claim 3wherein said elongated aperture means comprises a pair of slots, one ofsaid slots extending betWeen points closer to and further from saidterminal than any one of said conductors, the other of said slots beingarranged parallel to said one slot ahd having a length less than saidone slot, and wherein said conductive material is removed from said busband between said one slot near said closer point and said periphery ofsaid bus band.
 5. A window according to claim 4 wherein additionalconductive material is removed over a path between an end of said otherslot remote from said terminal and said bus band periphery to furtherincrease the current path between said terminal and said conductors. 6.A window according to claim 1 wherein each of said terminals isconnected to said bus bands between the ends, and said elongatedaperture means includes at least two individual slots, at least one ofsaid slots being arranged to one side of said terminal and at least oneof said slots being arranged to the other side of said terminal, andsaid selective removal of conductive material from said sheet beingcarried out over paths each extending substantially from a proximal endof each slot closest to said terminal to said periphery of said bus bandto increase the current path between said terminal and said conductors.